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Published: Mon, 5 Dec 2016

Background of the experiment:

When a gram of Potassium Nitrate is deposited in a milliliter of water the time taken for the substance to dissolve is called rate of solubility of the salt. This is measured generally by using experimental methods. The solubility has been found to be affected by many factors such as polarity of the solvent, mass of the solute, Temperature of the mixture etc. Hence to find the relationship between temperature and rate of solubility of Potassium Nitrate in water this experiment has been designed

Hypothesis:

The increase in temperature of the water makes the ions of Potassium Nitrate

(K+ and NO3-) gain Kinetic Energy which increases the speed with which the ions move between the solution and its solid state easily this increases the rate of solubility of the salt (KNO3) in water.

According to the second law of thermodynamics, the particles shifts from an ordered state to more disordered state this makes the solution more dispersed if the temperature increases.

As the temperature of water increases, the particles of solid Potassium Nitrate, KNO3, which are absorbing energy from its surrounding, start moving more easily between the solution and its solid state this can as, according to the second law of thermodynamics, the particles will shift to the more disordered state hence, more highly dispersed solution state. From this a prediction can be made that as the temperature of a KNO3 and water mixture increases, then the solubility of the KNO3 will also increase.

Variables:

Independent variable:

Temperature of the mixture is changed by using a refrigerator or a Bunsen burner measuring it with a digital thermometer for the best change in temperature.

Dependent variable:

the dependent variable will be the rate of solubility of Potassium Nitrate in water that will be measured at different temperatures

Control variables:

The volume of distilled water used to dissolve Potassium Nitrate in each beaker; this is controlled by taking constant volume of distilled water each trail by measuring it with a measuring cylinder.

Mass of Potassium Nitrate deposited into each beaker. The mass of the Potassium Nitrate dissolved is controlled by dissolving constant mass of Potassium Nitrate by measuring it with a digital balance.

The volume of Potassium Nitrate solution taken by the syringe from the different beakers to measure the rate of solubility. The volume of Potassium Nitrate solution taken by syringe is controlled by using a syringe with a facility of measuring the volume of the solution taken then keeping the volume taken same in all the syringes taken.

Weight of each 50ml beaker used. This is controlled by taking identical beakers each time

Methods and Reasons to control the variables:

The mass of Potassium Nitrate and the volume of distilled water introduced into each beaker should be recorded in order to allow the experimenter to determine the molar concentration of Potassium Nitrate in water. Since the same amount of water and Potassium Nitrate are used in each beaker throughout the whole experiment, these variables are the least likely to be the sources of errors.

All 6 solutions will be supersaturated in Potassium Nitrate. If the solutions were not supersaturated, an increase in solubility will not be detectable.

In order for all the solutions be subjected to the same experimental conditions, the same amount of time dedicated for stirring should be the same in all 6 100ml beakers.

The use of different syringes for the extraction of the Potassium Nitrate and distilled water solution from each beaker avoids the possibility of contradiction in the case where the same syringe was used in all 6 beakers.

The use of different syringes for the extraction of the Potassium Nitrate and distilled water solution from each beaker avoids the possibility of contradiction in the case where the same syringe was used in all 6 beakers.

The needle of the syringe should be placed at the midpoint between the surface of the solution and the bottom of the beaker upon extraction. This is because of it were placed at the surface of the solution some air partiNO3es might enter the syringe, and if it were placed at the bottom of the beaker some dissolvable partiNO3es might be extracted, thereby leading to an increase in the actual concentration of the dissolved salt.

The weight of each 50ml beaker (used for weighing the mass of dissolved Potassium Nitrate after the evaporation of water) should be recorded. If the experimenter were to weigh the mass of one beaker and take it as a default mass, the latter may be a source of error.

In order to minimize errors and to “place” the solutions in the same environment, the same volume should be extracted from each solution using the syringes.

After heating the extracted solution in the 50ml beaker for weighing purposes, some of the water might condense back into the liquid state (in the form droplets), thereby leading to an increase in the calculated weight of Potassium Nitrate. Therefore after evaporation has occurred and while the 50ml beaker is still hot, the beaker should be immediately weighed.

Apparatus:

Six Syringes

One Heating plate

Digital Thermometer

Water at 0°C

Bunsen Burner

Six distinctly labeled 50ml Beakers

One Digital Balance

Six Stirring Rods

Distilled Water

Six distinctly labeled 100ml Beaker

Procedure:

1.) Weigh each of the 50ml beakers labeled 1, 2, 3, 4, 5 and 6 and record their masses.

7.) Heat each of the 50 ml beakers until complete evaporation of the water occurs, and then immediately place each beaker on the balance and record the mass.

Data Collection:

By subtracting from the combined mass of (1) the salt residue from the evaporated extracted solution (m1) in the 50 ml beaker and the mass of the corresponding 50ml beaker (m2), the mass of the salt (m0) dissolved in the Sample solution can be obtained.

m0= m2- m1

The number of moles can be calculated, by using the formula

n= m0/MM,

Where m0 is the mass of the salt obtained in the sample solution and MM is the molar mass of the salt which is 58.44g mol-1

The number of moles is then divided by the volume of the extracted sample (40ml). The obtained concentration is then multiplied by a factor of 5, in order to get the concentration of the initial solution.

As the number of moles dissolved is calculated the rate of solubility can be estimated. By the formula

Rate of Solubility (s)

= Number of moles in salt residue (n) ÷ Time it is there in the liquid (t)

The table for the above procedure:

S.no

Temperature of the mixture

Mass of Salt residue from the evaporated extracted Solution

( g)

Number of Moles of the salt residue

(mol)

The concentration of initial Solution

(mol dm-3)

Rate of Solubility

(mol s-1)

1.

0°C

A

X

P

X t-1

2.

10°C

B

Y

Q

Y t-1

3.

20°C

C

Z

R

Z t-1

4.

30°C

D

W

S

W t-1

5.

40°C

E

V

T

V t-1

6.

50°C

F

U

O

U t-1

A

X

P

X t-1

This is according to the hypothesis formed in the starting of the experiment.

A graph can be drawn as follows for the variation of the rate of solubility with temperature of the mixture.

Number of moles of the salt residue

Temperature of the mixtureThe gradient of the below graph shows the variation of the rate of solubility with temperature of the mixture

The point to be noted here is that the graph is drawn by the theory from the hypothesis therefore it shows that the Temperature of the mixture is directly proportional to amount of salt dissolved in water.

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